This invention relates to a movable barrier such as a roll door having a two part guide follower that separates in response to a force in excess of a predetermined magnitude.
U.S. Pat. No. 5,025,847, assigned to the assignee of the present invention, discloses a roll door having a two part guide follower. This guide follower is designed to separate to allow the door and one part of the guide follower to be released from the other part of the guide follower in response to an excessive transverse force.
The system described in the above-identified patent has found widespread use, and has been found to significantly reduce the damage to overhead doors caused by unintended impacts, as for example with a moving forklift. In the event of such an impact, the guide follower separates, and the door is allowed to move transversely of the opening without damage to the door or to the guide followers. After the impact, the two part guide follower can readily be reassembled without extensive disassembly of the door mechanism and without special tools.
This represents a great improvement over the prior art approach in which the door was rigidly fastened to the guide follower. With this prior art approach the door could easily be damaged in the event of an impact, and such damage might require disassembly of the door or its mechanism and the replacement of bent or otherwise damaged parts. Of course in the event such parts were not kept on hand, such a repair could leave the door in an inoperable condition for an extended time.
The present invention is directed to further improvements in the basic system described in the above-identified patent, in order to make the two-part guide follower operate more consistently and more reliably, and to allow it to be reassembled more easily.